Entrained air refers to air dispersed throughout a liquid in the form of bubbles. Dissolved air is molecularly dispersed among the oil molecules. It is not entrained air bubbles dispersed in the liquid. Therefore, unlike entrained air, dissolved air has minimal effect on the properties of the dissolved air/oil mixture. Dissolved air does not become an issue until some of the dissolved air releases from solution, into the form of entrained air bubbles.

As a hydraulic system is operated, oil passes through various orifices and constrictions. These constrictions result in localized low-pressure areas on the downstream side of the constrictions. The low pressure causes some of the dissolved air to release into the form of entrained air. This entrained air causes serious problems such as:

Unpredictable decreases in the elastic modulus of hydraulic oil leads to errors in response rate of hydraulic actuators. The effect can be as little as extra time to complete a task or as critical as the loss of a rocket launcher.
Entrained air reduces pump capacity
The collapse of entrained air bubbles in high-pressure zones in the process leads to cavitation and errosive destruction..
Collapsing entrained air bubbles in oil generate enough heat to cause partial combustion of the oil, resulting in formation of carbonaceous deposits which can block oil passages.

There are many devices available for removing dissolved air from hydraulic oil. What is always missing with the operation of these devices is testing methods to determine when the dissolved air content has been removed to a safe level. PAPEC has measurement tools that are suitable for this task. PAPEC also has extensive engineering expertise available for consulting on these issues.

Contact us today to request information or learn more about our specialized testing instruments for entrained and dissolved air measurement.